1. Technical Field
The present invention relates to a method and system for motion prediction in general and, in particular to a method and system for predicting the motion of a ship. Still more particularly, the present invention relates to a method and system for a short-term prediction of future ship motion to provide visual cueing information to assist a pilot during a helicopter landing.
2. Description of the Prior Art
Landing a helicopter on the deck of a moving ship is not an easy task even when the weather is good and the water is calm. Deteriorating weather conditions and the associated increase in ship motion certainly make the helicopter landing on the deck of a moving ship almost an insurmountable task. Hence, in a broad sense, the safe operational envelope of a helicopter is partially limited by the weather conditions which, at times, is so adverse that all helicopter operations must be suspended.
Needlessly to say, in a Search and Rescue situation, many lives can be saved if the operational envelope of a helicopter can be safely extended without putting the helicopter pilot (and rescuer) at risk. In a combat role, the ability of a military helicopter to operate in various weather conditions always provides an advantage over the opposing force.
Currently, there are procedures that a ship command can employ for improving the safety of helicopter landing on the deck of a moving ship. These procedures include changing ship heading relative to the waves or changing ship speed for reducing ship motion. However, most of these procedures are performed under subjective human judgment along with some necessary conservative margins, which, more than often, results in larger ship heading changes, larger ship speed changes, or even premature suspensions of helicopter operations than theoretically necessary. Consequently, it would be desirable to provide an improved system for assisting a pilot to land a helicopter on the deck of a moving ship.
Typically, the landing of a helicopter on the deck of a moving ship may be divided into four distinct phases, as follows:
1. Initial approach: involves approaching to a distance of a few hundred meters from the moving ship. PA1 2. Tracking the ship: involves tracking a parallel course with the moving ship by taking up a position to the port side level with the flight deck at an altitude of around 20 meters. PA1 3. Hovering over the deck: involves hover-taxiing from the tracking position of phase 2 to a position over the deck. PA1 4. Final landing: involves the final vertical descent onto the deck of the ship.
Several minutes may be spent in phase 2 whilst the pilot judges the best moment to start phase 3. Phase 3 and phase 4 are normally conducted in a single smooth maneuver and, generally, it only takes about 30 seconds to perform both phase 3 and phase 4 completely. However, badly timed approaches may require the pilot to remain hovering in close proximity near the deck, waiting for a period of suitably benign ship motion. Such circumstances may result in sustaining phase 3 and phase 4 up to two minutes.
One objective of the present invention is to provide a short-term prediction of future ship motion during phase 2 for indicating when a period of quiescent ship motion is imminent such that the pilot is cued to start phase 3 and phase 4 as prompted. For the purpose of this invention, short-term is taken to mean in the order of 40 seconds into the future.